Why doesn't Firefox 4.0's Back Button doesn't work from home page or google search?

I just upgraded to firefox 4.0 tonight, and the back button isn't working correctly from my home page or from certain types of google searches. I can reproduce this problem every time by doing the following: 1) Open a new tab, and I get a blank page. 2) Select the Home button. I end up at http://www.google.com/ig 3) Go to the address bar and type in a new URI, and hit return I now leave my home page and go to the new page, but I cannot go back to my home page. Similar behavior happens if I do a google search from the quick search addres in the upper right hand corner. 1) start a new tab. 2) Enter a search term and hit enter 3) click on one of the search links, and you transition to the new page, but the back button doesn't work. It works fine if I do something like: 1) Open a new tab. 2) Enter google.com in the address bar and hit enter. 3) Do a search from GOOGLES search arae. 4) Click a search result link. This works fine for me.